The present invention relates to a connector for ribbon type optical fiber used for an optical fiber communication circuit system, whose cover or sheath is made of plastic material. More particularly, it relates to a connector for ribbon type optical fiber which can avoid deterioration of metal mold for molding a connector, and as the result it can reduce deterioration of aligning precision of an optical fiber caused by repeated attachment and detachment of the connector. The connector thus can much reduce an undesirable reflection return loss at joint locations where a number of optical fiber elements each having core and clad are jointed with each other.
In order to form an optical path in the optical fiber communication circuit system, optical fiber connectors are important elements.
FIGS. 7(a) and 7(b) show an example of a conventional connector for a ribbon type optical fiber, FIG. 7(b) being its side view and FIG. 7(a) is a plan view in section cut along the line C--C of FIG. 7(b).
At the central portion of a rectangular member 21 are provided a plurality of extremely small holes 23 for inserting optical fiber elements 22 in line and a hole 25 of a rectangular cross section into which cover portion 24 of the ribbon type optical fiber is inserted. At both sides of the line of the extremely small holes 23, there are provided alignment pin holes 26 through which alignment pins 27 are inserted.
The extremely small holes 23, the hole 25 of rectangular cross section and the alignment pin holes 26 are molded according to the plastic molding. This connector is easily assembled in that assembling is easily carried out by only inserting and bonding ribbon type optical fiber.
Core pins of a mold used for forming the extremely small holes 23 are very small in size, the order of 0.1254 mm.+-.0.005 mm in diameter. It is difficult to form the precise core pin. It has been usual to use the plastic material in which 50% or more, in weight, of glass fiber filament fillers are mixed for improving the strength and stability of size of molded products.
When the above mentioned material is used, core pins are easily scrubbed by molded holes. When injecting the material, high pressured plastic material is applied and core pins are easily worn out during the injecting operation by the glass fillers included in the material. For this reason the mold cannot fit for repeated use. broken and for this reason cannot be used for repeated use. Furthermore, in assembling the molded parts and the fiber elements, it is required to have a very small clearance between the optical fiber elements and the extremely small holes 23. It results in non-agreement between the fixed position of an optical fiber and the center position of a hole, which generates eccentric difference of 1-2 .mu.m. Thus loss of connection or insertion loss of connector is liable to become large.
In order to overcome the above-mentioned drawbacks, there have been proposed connectors of the type in which V-shaped grooves are provided for optical fiber elements.
FIGS. 8(a), 8(b) and 8(c) show an example of such a proposed connector. FIG. 8(b) shows a side and sectional view of the alignment V-shaped groove type connector and FIG. 8(a) is a D--D section of FIG. 8(b). FIG. 8(c) is an enlarged view of a V-shaped groove. In this example, a pair of members 30, 31 are lapped together and made integral, in both of which are provided four V-shaped grooves 28 for taking out a ribbon type optical fiber of four optical fiber elements 22 and two alignment grooves 29.
A metal mold for forming this connector has respective V-shaped groove forming portions at respective inner walls and it does not require any core pins as used in the prior art system as shown in FIGS. 7(a) and 7(b). Therefore, the die and the V-shaped groove forming portions may be designed without any fear of wearing with the molded body and the connector is free from wearing and since it does not receive any influences of wearing of the mold, it is good in stability of size.
In assembling, the optical fiber elements 22 are adhered and fixed by putting them between the member 30, 31 and therefore there is no problem of the alignment error by the clearance generated in the already explained prior art hole type connector.
However, the assembling efficiency of this alignment V-shaped groove type connector is inferior to the hole type connector, in that attachment of the optical fibers and assembly as well as integration of plural parts has to be carried out simultaneously, and therefore many steps of operations and the skill are required.
As mentioned above, alignment of a pair of connectors of the ribbon type optical fiber has been made mainly according to the alignment pin type connector shown in FIGS. 7(a) and 7(b) and the alignment V-shaped groove type connector as shown in FIGS. 8(a), 8(b) and 8(c).
The alignment pin type connector uses the material of connector of plastic including glass and so the alignment holes and alignment pins of the die are easily abraded by repeating the injection of resin material, taking off the product therefrom. Thus the precision of alignment is liable to be deteriorated
On the other hand, the alignment V-shaped groove type connector has similar drawbacks, though little, that after the repeat of attaching and detaching, the alignment V-groove portion and protrusions of the V-shaped grooves are worn out.
Since both types have no particular means for recovering or amending the abrasion in the systems, there has been problems for their durability for attaching and detaching.
An object of the present invention is to solve the above problems and to provide a ribbon type optical fiber connector which is excellent in assembling operation, can avoid the generation of an error in mounting position of the optical fiber and which can avoid any abrasion of grooves due to the repeated attaching and detaching operations.